U.S. patent application number 11/442860 was filed with the patent office on 2007-12-06 for method and apparatus to improve closed loop transmit diversity modes performance via interference suppression in a wcdma network equipped with a rake receiver.
Invention is credited to Severine Catreux-Erceg, Vinko Erceg.
Application Number | 20070280147 11/442860 |
Document ID | / |
Family ID | 38434534 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070280147 |
Kind Code |
A1 |
Catreux-Erceg; Severine ; et
al. |
December 6, 2007 |
Method and apparatus to improve closed loop transmit diversity
modes performance via interference suppression in a WCDMA network
equipped with a rake receiver
Abstract
Methods and systems for processing signals in a wireless
communication system are disclosed. Aspects of the method may
include calculating at a receiver, a plurality of
signal-to-interference-plus-noise ratio (SINR) values for a
wireless signal, which is received from a transmitter, based on a
corresponding plurality of weight values. A maximum one of the
calculated plurality of SINR values may be determined. At least one
weight value including one of the corresponding plurality of weight
values may be fed back to the transmitter. The at least one weight
value including one of the corresponding plurality of weight values
may be associated with the determined maximum one of the calculated
plurality of SINR values. The at least one weight value including
one of the corresponding plurality of weight values may be
communicated to the transmitter via at least one downlink
communication channel.
Inventors: |
Catreux-Erceg; Severine;
(Cardiff, CA) ; Erceg; Vinko; (Cardiff,
CA) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET, SUITE 3400
CHICAGO
IL
60661
US
|
Family ID: |
38434534 |
Appl. No.: |
11/442860 |
Filed: |
May 30, 2006 |
Current U.S.
Class: |
370/318 |
Current CPC
Class: |
H04B 7/0634 20130101;
H04B 17/336 20150115 |
Class at
Publication: |
370/318 |
International
Class: |
H04B 7/185 20060101
H04B007/185 |
Claims
1. A method for processing signals in a wireless communication
system, the method comprising: calculating at a receiver, a
plurality of signal-to-interference-plus-noise ratio (SINR) values
for a wireless signal, which is received from a transmitter, based
on a corresponding plurality of weight values; determining a
maximum one of said calculated plurality of SINR values; and
feeding back to said transmitter, at least one weight value
comprising one of said corresponding plurality of weight values,
which is associated with said determined maximum one of said
calculated plurality of SINR values.
2. The method according to claim 1, further comprising
communicating said at least one weight value comprising one of said
corresponding plurality of weight values to said transmitter via at
least one uplink communication channel.
3. The method according to claim 2, wherein said at least one
uplink communication channel comprises a high-speed dedicated
physical control channel (HS-DPCCH).
4. The method according to claim 1, wherein each of said plurality
of SINR values comprises at least one inter-path interference (IPI)
value.
5. The method according to claim 1, wherein said plurality of
weight values comprises at least one closed loop mode 1 (CLM1)
weight value.
6. The method according to claim 1, wherein said plurality of
weight values comprises at least one closed loop mode 2 (CLM2)
weight value.
7. The method according to claim 1, further comprising: calculating
said plurality of SINR values for said wireless signal utilizing at
least one phase shift value; and selecting said at least one phase
shift value from a range of [0.degree.; 360.degree.] utilizing at
least one quantized step value.
8. The method according to claim 1, further comprising calculating
said plurality of SINR values for said wireless signal utilizing at
least one of: a phase shift value and an amplitude value.
9. The method according to claim 1, further comprising acquiring at
said receiver, at least one of: channel state information and
system geometry information for said wireless signal.
10. The method according to claim 9, further comprising calculating
at said receiver, said plurality of SINR values for said wireless
signal, based on at least one of: said channel state information
and said system geometry information.
11. A system for processing signals in a wireless communication
system, the system comprising: at least one processor integrated
within a receiver that enables calculation at a receiver of a
plurality of SINR values for a wireless signal, which is received
from a transmitter, based on a corresponding plurality of weight
values; said at least one processor enables determination of a
maximum one of said calculated plurality of SINR values; and said
at least one processor enables feeding back to said transmitter, at
least one weight value comprising one of said corresponding
plurality of weight values, which is associated with said
determined maximum one of said calculated plurality of SINR
values.
12. The system according to claim 11, wherein said at least one
processor enables communication of said at least one weight value
comprising one of said corresponding plurality of weight values to
said transmitter via at least one uplink communication channel.
13. The system according to claim 12, wherein said at least one
uplink communication channel comprises a high-speed dedicated
physical control channel (HS-DPCCH).
14. The system according to claim 11, wherein each of said
plurality of SINR values comprises at least one inter-path
interference (IPI) value.
15. The system according to claim 11, wherein said plurality of
weight values comprises at least one closed loop mode 1 (CLM1)
weight value.
16. The system according to claim 11, wherein said plurality of
weight values comprises at least one closed loop mode 2 (CLM2)
weight value.
17. The system according to claim 11, wherein said at least one
processor enables calculation of said plurality of SINR values for
said wireless signal utilizing at least one phase shift value.
18. The system according to claim 17, wherein said at least one
processor enables selection of said at least one phase shift value
from a range of [0.degree.; 360.degree.] utilizing at least one
quantized step value.
19. The system according to claim 11, wherein said at least one
processor enables acquiring at said receiver of at least one of:
channel state information and system geometry information for said
wireless signal.
20. The system according to claim 19, wherein said at least one
processor enables calculation at said receiver of said plurality of
SINR values for said wireless signal, based on at least one of:
said channel state information and said system geometry
information.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY
REFERENCE
[0001] [Not Applicable]
FIELD OF THE INVENTION
[0002] Certain embodiments of the invention relate to the
processing of wireless communication signals. More specifically,
certain embodiments of the invention relate to a method and
apparatus to improve closed loop transmit diversity modes
performance via interference suppression in a WCDMA network
equipped with a RAKE receiver.
BACKGROUND OF THE INVENTION
[0003] Mobile communications has changed the way people communicate
and mobile phones have been transformed from a luxury item to an
essential part of every day life. The use of mobile phones is today
dictated by social situations, rather than hampered by location or
technology. While voice connections fulfill the basic need to
communicate, and mobile voice connections continue to filter even
further into the fabric of every day life, the mobile Internet is
the next step in the mobile communication revolution. The mobile
Internet is poised to become a common source of everyday
information, and easy, versatile mobile access to this data will be
taken for granted.
[0004] Third generation (3G) cellular networks have been
specifically designed to fulfill these future demands of the mobile
Internet. As these services grow in popularity and usage, factors
such as cost efficient optimization of network capacity and quality
of service (QoS) will become even more essential to cellular
operators than it is today. These factors may be achieved with
careful network planning and operation, improvements in
transmission methods, and advances in receiver techniques. To this
end, carriers need technologies that will allow them to increase
downlink throughput and, in turn, offer advanced QoS capabilities
and speeds that rival those delivered by cable modem and/or DSL
service providers. In this regard, networks based on wideband CDMA
(WCDMA) technology may make the delivery of data to end users a
more feasible option for today's wireless carriers.
[0005] The GPRS and EDGE technologies may be utilized for enhancing
the data throughput of present second generation (2G) systems such
as GSM. The GSM technology may support data rates of up to 14.4
kilobits per second (Kbps), while the GPRS technology, introduced
in 2001, may support data rates of up to 115 Kbps by allowing up to
8 data time slots per time division multiple access (TDMA) frame.
The GSM technology, by contrast, may allow one data time slot per
TDMA frame. The EDGE technology, introduced in 2003, may support
data rates of up to 384 Kbps. The EDGE technology may utilizes 8
phase shift keying (8-PSK) modulation for providing higher data
rates than those that may be achieved by GPRS technology. The GPRS
and EDGE technologies may be referred to as "2.5G"
technologies.
[0006] The UMTS technology, introduced in 2003, with theoretical
data rates as high as 2 Mbps, is an adaptation of the WCDMA 3G
system by GSM. One reason for the high data rates that may be
achieved by UMTS technology stems from the 5 MHz WCDMA channel
bandwidths versus the 200 KHz GSM channel bandwidths. The HSDPA
technology is an Internet protocol (IP) based service, oriented for
data communications, which adapts WCDMA to support data transfer
rates on the order of 10 megabits per second (Mbits/s). Developed
by the 3G Partnership Project (3GPP) group, the HSDPA technology
achieves higher data rates through a plurality of methods. For
example, many transmission decisions may be made at the base
station level, which is much closer to the user equipment as
opposed to being made at a mobile switching center or office. These
may include decisions about the scheduling of data to be
transmitted, when data is to be retransmitted, and assessments
about the quality of the transmission channel. The HSDPA technology
may also utilize variable coding rates. The HSDPA technology may
also support 16-level quadrature amplitude modulation (16-QAM) over
a high-speed downlink shared channel (HS-DSCH), which permits a
plurality of users to share an air interface channel
[0007] In some instances, HSDPA may provide a two-fold improvement
in network capacity as well as data speeds up to five times (over
10 Mbit/s) higher than those in even the most advanced 3G networks.
HSDPA may also shorten the roundtrip time between network and
terminal, while reducing variances in downlink transmission delay.
These performance advances may translate directly into improved
network performance and higher subscriber satisfaction. Since HSDPA
is an extension of the GSM family, it also builds directly on the
economies of scale offered by the world's most popular mobile
technology. HSDPA may offer breakthrough advances in WCDMA network
packet data capacity, enhanced spectral and radio access networks
(RAN) hardware efficiencies, and streamlined network
implementations. Those improvements may directly translate into
lower cost-per-bit, faster and more available services, and a
network that is positioned to compete more effectively in the
data-centric markets of the future.
[0008] The capacity, quality and cost/performance advantages of
HSDPA yield measurable benefits for network operators, and, in
turn, their subscribers. For operators, this backwards-compatible
upgrade to current WCDMA networks is a logical and cost-efficient
next step in network evolution. When deployed, HSDPA may co-exist
on the same carrier as the current WCDMA Release 99 services,
allowing operators to introduce greater capacity and higher data
speeds into existing WCDMA networks. Operators may leverage this
solution to support a considerably higher number of high data rate
users on a single radio carrier. HSDPA makes true mass-market
mobile IP multimedia possible and will drive the consumption of
data-heavy services while at the same time reducing the
cost-per-bit of service delivery, thus boosting both revenue and
bottom-line network profits. For data-hungry mobile subscribers,
the performance advantages of HSDPA may translate into shorter
service response times, less delay and faster perceived
connections. Users may also download packet-data over HSDPA while
conducting a simultaneous speech call.
[0009] HSDPA may provide a number of significant performance
improvements when compared to previous or alternative technologies.
For example, HSDPA extends the WCDMA bit rates up to 10 Mbps,
achieving higher theoretical peak rates with higher-order
modulation (16-QAM) and with adaptive coding and modulation
schemes. The maximum QPSK bit rate is 5.3 Mbit/s and 10.7 Mbit/s
with 16-QAM. Theoretical bit rates of up to 14.4 Mbit/s may be
achieved with no channel coding. The terminal capability classes
range from 900 kbit/s to 1.8 Mbit/s with QPSK modulation, and 3.6
Mbit/s and up with 16-QAM modulation. The highest capability class
supports the maximum theoretical bit rate of 14.4 Mbit/s.
[0010] However, implementing advanced wireless technologies such as
WCDMA and/or HSDPA may still require overcoming some architectural
hurdles. For example, the RAKE receiver is the most commonly used
receiver in CDMA systems, mainly due to its simplicity and
reasonable performance and WCDMA Release 99 networks are designed
so that RAKE receivers may be used. A RAKE receiver contains a bank
of spreading sequence correlators, each receiving an individual
multipath. A RAKE receiver operates on multiple discrete paths. The
received multipath signals may be combined in several ways, from
which maximum ratio combining (MRC) is preferred in a coherent
receiver. However, a RAKE receiver may be suboptimal in many
practical systems. For example, its performance may degrade from
multiple access interference (MAI), that is, interference induced
by other users in the network.
[0011] In the case of a WCDMA downlink, MAI may result from
intercell and intracell interference. The signals from neighboring
base stations compose intercell interference, which is
characterized by scrambling codes, channels and angles of arrivals
different from the desired base station signal. Spatial
equalization may be utilized to suppress inter-cell interference.
In a synchronous downlink application, employing orthogonal
spreading codes, intracell interference may be caused by multipath
propagation. In some instances, intracell interference may comprise
inter-path interference (IPI). IPI may occur or RAKE fingers
generated when one or more paths, or RAKE "fingers," interfere with
other paths within the RAKE receiver. Due to the non-zero
cross-correlation between spreading sequences with arbitrary time
shifts, interference occurs between propagation paths (or RAKE
fingers) after despreading, causing MAI. The level of intracell
interference depends strongly on the channel response. In nearly
flat fading channels, the physical channels remain almost
completely orthogonal and intra-cell interference does not have any
significant impact on the receiver performance. On the other hand,
the performance of the RAKE receiver may be severely deteriorated
by intra-cell interference in frequency selective channels.
Frequency selectivity is common for the channels in WCDMA
networks.
[0012] Due to the difficulties faced when non-linear channel
equalizers are applied to the WCDMA downlink, detection of the
desired physical channel with a non-linear equalizer may result in
implementing an interference canceller or optimal multi-user
receiver. Both types of receivers may be prohibitively complex for
mobile terminals and may require information not readily available
at the mobile terminal. Alternatively, the total base station
signal may be considered as the desired signal. However, non-linear
equalizers rely on prior knowledge of the constellation of the
desired signal, and this information is not readily available at
the WCDMA terminal. The constellation of the total base station
signal, that is, sum of all physical channels, is a high order
quadrature amplitude modulation (QAM) constellation with uneven
spacing. The spacing of the constellation changes constantly due to
transmission power control (TPC) and possible power offsets between
the control data fields, time-multiplexed to the dedicated physical
channels. The constellation order may also frequently change due to
discontinuous transmission. This makes an accurate estimation of
the constellation very difficult.
[0013] In this regard, the use of multiple transmit and/or receive
antennas may result in an improved overall system performance.
These multi-antenna configurations, also known as smart antenna
techniques, may be utilized to mitigate the negative effects of
multipath and/or signal interference on signal reception. It is
anticipated that smart antenna techniques may be increasingly
utilized both in connection with the deployment of base station
infrastructure and mobile subscriber units in cellular systems to
address the increasing capacity demands being placed on those
systems. These demands arise, in part, from a shift underway from
current voice-based services to next-generation wireless multimedia
services that provide voice, video, and data communication.
[0014] The utilization of multiple transmit and/or receive antennas
is designed to introduce a diversity gain and to suppress
interference generated within the signal reception process. Such
diversity gains improve system performance by increasing received
signal-to-noise ratio, by providing more robustness against signal
interference, and/or by permitting greater frequency reuse for
higher capacity. In communication systems that incorporate
multi-antenna receivers, a set of M receive antennas may be
utilized to null the effect of (M-1) interferers, for example.
Accordingly, N signals may be simultaneously transmitted in the
same bandwidth using N transmit antennas, with the transmitted
signal then being separated into N respective signals by way of a
set of N antennas deployed at the receiver. Systems that utilize
multiple transmit and receive antennas may be referred to as
multiple-input multiple-output (MIMO) systems. One attractive
aspect of multi-antenna systems, in particular MIMO systems, is the
significant increase in system capacity that may be achieved by
utilizing these transmission configurations. For a fixed overall
transmitted power, the capacity offered by a MIMO configuration may
scale with the increased signal-to-noise ratio (SNR). For example,
in the case of fading multipath channels, a MIMO configuration may
increase system capacity by nearly M additional bits/cycle for each
3-dB increase in SNR.
[0015] However, the widespread deployment of multi-antenna systems
in wireless communications, particularly in wireless handset
devices, has been limited by the increased cost that results from
increased size, complexity, and power consumption. Providing a
separate RF chain for each transmit and receive antenna is a direct
factor that increases the cost of multi-antenna systems. As the
number of transmit and receive antennas increases, the system
complexity, power consumption, and overall cost may increase. In
addition, conventional methods of signal processing at the receiver
side of a wireless communication system do not take into account
outside interference as well as IPI resulting within a multipath
fading environment. This poses problems for mobile system designs
and applications.
[0016] Further limitations and disadvantages of conventional and
traditional approaches will become apparent to one of skill in the
art, through comparison of such systems with some aspects of the
present invention as set forth in the remainder of the present
application with reference to the drawings.
BRIEF SUMMARY OF THE INVENTION
[0017] A method and/or apparatus to improve closed loop transmit
diversity modes performance via interference suppression in a WCDMA
network equipped with a RAKE receiver, substantially as shown in
and/or described in connection with at least one of the figures, as
set forth more completely in the claims.
[0018] These and other advantages, aspects and novel features of
the present invention, as well as details of an illustrated
embodiment thereof, will be more fully understood from the
following description and drawings.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0019] FIG. 1A illustrates an exemplary wireless distributed
architecture that achieves low delay link adaptation, in connection
with an embodiment of the invention.
[0020] FIG. 1B is a diagram illustrating an exemplary HSDPA channel
structure, which may be utilized in connection with an embodiment
of the invention.
[0021] FIG. 2 is a block diagram of an exemplary wireless
communication system with receiver channel estimation, in
accordance with an embodiment of the invention.
[0022] FIG. 3A is a first graph illustrating closed loop transmit
diversity modes performance via interference suppression in a
wireless system using a RAKE receiver, in accordance with an
embodiment of the invention.
[0023] FIG. 3B is a second graph illustrating closed loop transmit
diversity modes performance via interference suppression in a
wireless system using a RAKE receiver, in accordance with an
embodiment of the invention.
[0024] FIG. 3C is a third graph illustrating closed loop transmit
diversity modes performance via interference suppression in a
wireless system using a RAKE receiver, in accordance with an
embodiment of the invention.
[0025] FIG. 3D is a fourth graph illustrating closed loop transmit
diversity modes performance via interference suppression in a
wireless system using a RAKE receiver, in accordance with an
embodiment of the invention.
[0026] FIG. 4 is a flow diagram illustrating exemplary steps for
processing wireless signals in a WCDMA network equipped with a RAKE
receiver, in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] Certain embodiments of the invention may be found in a
method and/or apparatus to improve closed loop transmit diversity
modes performance via interference suppression in a WCDMA network
equipped with a RAKE receiver. Aspects of the method may include
calculating at a receiver, a plurality of
signal-to-interference-plus-noise ratio (SINR) values for a
wireless signal, which is received from a transmitter, based on a
corresponding plurality of weight values. A maximum one of the
calculated plurality of SINR values may be determined. At least one
weight value comprising one of the corresponding plurality of
weight values may be fed back to the transmitter. The at least one
weight value comprising one of the corresponding plurality of
weight values may be associated with the determined maximum one of
the calculated plurality of SINR values. The weight value
comprising one of the corresponding plurality of weight values may
be communicated to the transmitter via at least one uplink
communication channel. Each of the plurality of SINR values may
comprise an inter-path interference (IPI) value. Channel state
information and/or system geometry information for the wireless
signal may be acquired at the receiver. The plurality of SINR
values for the wireless signal may be calculated at the receiver
based on the channel state information and/or the system geometry
information.
[0028] FIG. 1A illustrates an exemplary wireless distributed
architecture that achieves low delay link adaptation, in connection
with an embodiment of the invention. Referring to FIG. 1A, there is
shown user equipment (UE) 110 and 112 and a base station (BS) 114.
A WCDMA data connection, such as HSDPA may be built on a
distributed architecture that achieves low delay link adaptation by
placing key processing at the BS 114 and thus closer to the air
interface as illustrated. Accordingly, the MAC layer at the BS 114
is moved from Layer 2 to Layer 1, which implies that the systems
may respond in a much faster manner with data access. Fast link
adaptation methods, which are generally well established within
existing GSM/EDGE standards, include fast physical layer (L1)
retransmission combining and link adaptation techniques. These
techniques may deliver significantly improved packet data
throughput performance between the mobile terminals 110 and 112 and
the BS 114.
[0029] The HSDPA technology employs several important new
technological advances. Some of these may comprise scheduling for
the downlink packet data operation at the BS 114, higher order
modulation, adaptive modulation and coding, hybrid automatic repeat
request (HARQ), physical layer feedback of the instantaneous
channel condition, and a new transport channel type known as
high-speed downlink shared channel (HS-DSCH) that allows several
users to share the air interface channel. When deployed, HSDPA may
co-exist on the same carrier as the current WCDMA and UMTS
services, allowing operators to introduce greater capacity and
higher data speeds into existing WCDMA networks. HSDPA replaces the
basic features of WCDMA, such as variable spreading factor and fast
power control, with adaptive modulation and coding, extensive
multicode operation, and fast and spectrally efficient
retransmission strategies.
[0030] In current-generation WCDMA networks, power control dynamics
are on the order of 20 dB in the downlink and 70 dB in the uplink.
WCDMA downlink power control dynamics are limited by potential
interference between users on parallel code channels and by the
nature of WCDMA base station implementations. For WCDMA users close
to the base station, power control may not reduce power optimally,
and reducing power beyond the 20 dB may therefore have only a
marginal impact on capacity. HSDPA, for example, utilizes advanced
link adaptation and adaptive modulation and coding (AMC) to ensure
all users enjoy the highest possible data rate. AMC therefore
adapts the modulation scheme and coding to the quality of the
appropriate radio link.
[0031] Furthermore, WCDMA networks, including HSDPA networks may
utilize closed-loop transmit diversity mode (CLTDM) to improve the
performance of a wireless system. For example, the BS 114 may be
equipped with one or more transmit antennas, each of which may
transmit one or more weighted versions of the same signal. The UE
110 and 112 may comprise a RAKE receiver which may process the
received wireless signal. The weights used by the BS 114 may be
determined by the user equipment (UE) 110 and/or 112, and may be
communicated to the BS 114 via a feedback control message. In a
WCDMA system that uses a combination of CLTDM at the transmitter
and RAKE at the receiver, the complex value of the weights may be
computed within the UE 110 and/or 112 so as to optimize received
signal processing performance at the output of the RAKE
receivers.
[0032] In closed-loop mode 1 (CLM1) and closed-loop mode 2 (CLM2)
transmit diversity scenarios two weights (w1 and w2) may be
communicated from the UE 110 and/or 112 to the transmitter in the
BS 114. In a CLM1 scenario, the weight value w1 may be a constant,
such as 1, and the weight value w2 may be determined within the
RAKE receiver of the UE 110 and/or 112. The weight value w2 may
then be communicated to the transmitter in the BS 114. In a CLM2
scenario, both weight values w1 and w2 may be determined within the
RAKE receiver of the UE 110 and/or 112. The weight values w1 and w2
may then be communicated to the transmitter in the BS 114.
[0033] In some instances, the weight values w1 and/or w2 may be
computed so that the received power of the UE 110 and/or 112 is
maximized. An example of such weight computation may be read in the
"3G Partnership Project" (3GPP) specification, TS 25.214, entitled
"Physical Layer Procedures (FDD)," which is hereby incorporated by
reference herein in its entirety.
[0034] In one embodiment of the invention, the UE 110 and/or 112
may calculate the weight values w1 and/or w2 so that SINR at the
output of the RAKE receiver is maximized. In this regard, the SINR
may take into account inter-path-interference (IPI) that is
internal to the communication path between the UE 110 and/or 112
and the BS 114. By maximizing SINR during the weight value
generation process in a multipath fading environment, RAKE receiver
performance and CLTDM performance may be further improved.
[0035] FIG. 1B is a diagram illustrating an exemplary HSDPA channel
structure, which may be utilized in connection with an embodiment
of the invention. Referring to FIG. 1B, three additional channels
may be used to support HSDPA connection between the base station
102c and the UE 104c. A high-speed downlink shared channel
(HS-DSCH) 106c and a high speed shared control channel (HS-SCCH)
108c may be used on the downlink between the base station 102c and
the UE 104c. A high-speed dedicated physical control channel
(HS-DPCCH) 110c may be used on the uplink between the UE 104c and
the base station 102c.
[0036] The HS-DPCCH 110c may be used as a signaling channel that
carries acknowledge (ACK) and non-acknowledge (NACK) signals and
measurement reports. The HS-DSCH 106c may comprise a plurality of
high-speed physical downlink shared channel (HS-PDSCH) and may be
used to carry user data. The HS-SCCH 108c may be used to carry
exemplary control information, such as modulation, HARQ
redundancy/constellation version, HARQ processor ID, new data
indication, index of the transport block size, and/or user
equipment (UE) identity information corresponding to the data
carried in the HS-DSCH channel 106c. The UE 104c may use several
physical channel-related parameters to indicate to the base station
102c its capability to support the HSDPA services.
[0037] In one embodiment of the invention, the wireless system 100c
may utilize CLTDM to improve signal processing at the UE 104c. In
this regard, one or more weight values may be calculated at the UE
104c and may be communicated to the base station 102c via the
HS-DPCCH 110c. The UE 104c may determine the one or more weights
by, for example, maximizing signal-to-interference-plus-noise ratio
(SINR) at the output of RAKE receiver within the UE 104c.
[0038] FIG. 2 is a block diagram of an exemplary wireless
communication system with receiver channel estimation, in
accordance with an embodiment of the invention. Referring to FIG.
2, the wireless communication system 200 may comprise a dedicated
physical channel (DPCH) block 226, a plurality of mixers 228, 230
and 232, a first combiner 234, a second combiner 236, a first
transmit antenna (Tx_1) 238, an additional transmit antenna (Tx_2)
240, and a first receive antenna (Rx_1) 206. The wireless
communication system 200 may further comprise an RF block 214, a
chip matching filter (CMF) 216, a cluster path processor (CPP) 218,
a baseband (BB) processor 220, and a weight value processing block
(WVPB) 221. Furthermore, the receive antenna 206, the RF block 214,
the CMF 216, the CPP 218, the BB processor 220, and the WVPB 221
may be located within user equipment (UE) 202a. The UE 202a may be,
for example, a wireless phone or another wireless device such as a
SmartPhone or PDA with cell phone capabilities.
[0039] The DPCH 226 may comprise suitable logic, circuitry, and/or
code that may be adapted to receive a plurality of input channels,
for example, a dedicated physical control channel (DPCCH) and a
dedicated physical data channel (DPDCH). The DPCH 226 may be
adapted to simultaneously control the power on each of the DPCCH
and DPDCH channels. The mixer 228 may comprise suitable logic
and/or circuitry that may be adapted to multiply the output of DPCH
226 with a spread and/or scramble signal to generate a spread
complex-valued signal that may be transferred to the inputs of the
mixers 230 and 232.
[0040] The mixers 230 and 232 may comprise suitable logic and/or
circuitry that may be adapted to multiply the spread complex-valued
signal from the mixer 228 by the closed loop 1 (CL1) and closed
loop 2 (CL2) transmit diversity weight factors W.sub.1 and W.sub.2
respectively. Closed loop transmit diversity modes (CLTDM) are
described in the 3.sup.rd Generation Project Partnership (3GPP),
Technical Specification Group Radio Access Network, Physical Layer
Procedures (FDD), Release 6 (3GPP TS 25.214 V5.5.0, 2003-06), which
document is incorporated herein by reference in its entirety. For
example, the weight factors W.sub.1 and W.sub.2 may correspond to
phase and/or amplitude component feedback adjustments that may be
generated by the receiver based on the type of space-time coding
that is used. This approach may correspond to, for example, closed
loop transmit diversity as currently being used in WCDMA. In this
regard, a closed loop processing block may be utilized to transfer
the weight factors or parameters that correspond to those weight
factors to the transmitter via an uplink feedback process utilizing
the feedback communication link 201a, for example.
[0041] The output of the mixer 230 may be transferred to the first
combiner 234 and the output of the mixer 232 may be transferred to
the second combiner 236. The first and second combiners 234 and 236
may comprise suitable logic, circuitry, and/or code that may be
adapted to add or combine the outputs generated by mixers 230 and
232 with a common pilot channel 1 (CPICH1) signal and a common
pilot channel 2 (CPICH2) signal respectively. The CPICH1 signal and
CPICH2 signals may comprise fixed channelization code allocation
and may be utilized to measure the signal phase and amplitude and
strength of the propagation channels between the transmit antennas
and the receive antennas.
[0042] The first transmit antenna, Tx_1 238, and the additional or
second transmit antenna, Tx_2 240, may comprise suitable hardware
that may be adapted to transmit a plurality of SC communication
signals, ST, from a wireless transmitter device. The first receive
antenna, Rx_1 206 may comprise suitable hardware that may be
adapted to receive at least a portion of the transmitted SC
communication signals in a wireless receiver device as SR. The
propagation channels that corresponds to the paths taken by the SC
communication signals transmitted from the transmit antennas Tx_1
238 and Tx_2 240 and received by the receive antenna Rx_1 206 may
be represented by h.sub.1 and h.sub.2 respectively. In this regard,
h.sub.1 and h.sub.2 may represent the actual time varying impulse
responses of the radio frequency (RF) paths taken by the SC
communication signals transmitted from the transmit antennas Tx_1
238 and Tx_2 240 and received by the receive antenna Rx_1 206.
[0043] In some instances, a wireless transmitter device comprising
dual transmit antennas may be adapted to periodically transmit
calibration and/or pilot signals that may be utilized by a 1-Rx
antenna wireless receiver device to determine estimates of h.sub.1
and h.sub.2. The 2-Tx and 1-Rx antennas wireless communication
system 200 in FIG. 2 may represent a Multiple Input Single Output
(MISO) communication system whereby the diversity gain may be
increased for the transmitted data.
[0044] The RF block 214 may comprise suitable logic and/or
circuitry that may be adapted to process the combined received SC
communication signal, s.sub.R. The RF block 214 may perform, for
example, filtering, amplification, and/or analog-to-digital (A/D)
conversion operations. The CMF 216 may comprise suitable logic,
circuitry, and/or code that may be adapted to operate as a
matched-filter on the digital output from the RF block 214. The
output of the CMF 216 may be transferred, for example, to the CPP
218 and/or to the BB processor 220 for further processing. The CPP
218 may comprise suitable logic, circuitry, and/or code that may be
adapted to process the filtered output of the CMF 216 to determine
a first baseband combined channel estimate, h.sub.1, which may
comprise information regarding propagation channels h.sub.1. The
CPP 218 may also be adapted to process the filtered output of the
CMF 216 to determine a second baseband combined channel estimate,
h.sub.2, which may comprise information regarding propagation
channels h.sub.2. In this regard, the CPP 218 may process the
received signals in clusters. The CPP 218 may also be adapted to
generate a lock indicator signal that may be utilized by, for
example, the BB processor 220 as an indication of whether the
channel estimates are valid. The BB processor 220 may comprise
suitable logic, circuitry, and/or code that may be adapted to
digitally process the filtered output of the CMF 216 to determine
an estimate of the transmitted SC communication signals,
s.sub.T.
[0045] The WVPB 221 may comprise suitable logic, circuitry, and/or
code that may be adapted to receive the first and second baseband
combined channel estimates, h.sub.1 and h.sub.2, from the BB
processor 220 or from the CPP 218 and generate the weight values w1
and w2, which may be communicated to the transmitter 200a via the
dedicated physical control channel (DPCCH) 201a. Additionally, the
WVPB 221 may comprise suitable logic, circuitry, and/or code that
may be adapted to communicate the weights values w1 and w2 to the
BB processor 220 which may use them to determine an estimate of the
transmitted SC communication signals, s.sub.T.
[0046] In operation, the wireless communication system 200 may
utilize closed loop mode 1 (CLM1) or closed loop mode 2 (CLM2)
transmit diversity. In this regard, the WVPB 221 may generate one
or more weight values, for example w1 and w2, which may be fed back
to the transmit side 200a via the feedback communication path 201a.
For example, if CLM1 is utilized, the weight factor w1 may comprise
a constant scalar, such as 1, and the weight factor w2 may comprise
a complex value, such as a corresponding phase adjustment .phi.. If
the wireless communication system 200 utilizes CLM2, both w1 and w2
may assume different values.
[0047] In some instances, the wireless communication system 200 may
utilize CLM1. The WVPB 221 within the UE 202a may compute the phase
adjustment, w.sub.2=e.sup.j.phi. once for every slot so that
receive power at the UE 202a is maximized. An example of such
weight computation may be read in the "3G Partnership Project"
(3GPP) specification, TS 25.214, entitled "Physical Layer
Procedures (FDD)," which is hereby incorporated by reference in its
entirety in instances when a non-soft handover occurs within the
wireless communication system 200, the computation of feedback
information by the WVPB 221 may be accomplished by, for example,
solving for a weight vector, w, that maximizes:
P=w.sup.HH.sup.Hw
where
H=[h.sub.1h.sub.2] and w=[w.sub.1,w.sub.2].sup.T
and where the column vectors h.sub.1 and h.sub.2 represent the
estimated channel impulse responses for the transmission antennas 1
and 2, of length equal to the length of the channel impulse
response. The estimated channel impulse responses may be received
by the WVPB 221 from the CPP 218.
[0048] In another embodiment of the invention, the WVPB 221 within
the UE 202a may compute one or more of the weight factors w1 and w2
to maximize the received SINR at the output of the RAKE receiver
within the UE 202a. In this regard, the SINR may take into account
the inter-path-interference (IPI) that is internal to the
communication path between the UE 202a and the transmit side 200a.
By maximizing SINR during the weight value generation process in a
multipath fading environment, RAKE receiver performance and CLTDM
performance may be further improved.
[0049] In instances where CLM1 is utilized by the wireless
communication system 200, the weight value w1 may equal a constant,
such as 1. The received signal at finger i of the RAKE receiver
within the UE 202a may be represented by the equation:
r i = P s 2 x ( h 1 i + w 2 h 2 i ) + n i , ( 1. ) ##EQU00001##
Where P.sub.s may comprise the transmit signal power and x may
comprise a transmitted complex symbol. For example, the transmitted
complex symbol may be quadrature amplitude modulation
(QAM)-modulated and may be represented as (1+j). The factor of 1/2
may be used to account for the total transmit power split between
the 2 transmit antennas 238 and 240. The variables h.sub.1i and
h.sub.2i may comprise the channel gains at finger i for transmit
antennas 238 and 240 respectively, and n.sub.i may comprise a
complex random variable Gaussian distributed, with zero mean and
variance .sigma..sub.i.sup.2. The variance .sigma..sub.i.sup.2 may
comprise a measure of the additive noise and IPI, for example.
[0050] If IPI is present within the wireless communication system
200, the variance .sigma..sub.i.sup.2 may be represented by the
equation:
.sigma. i 2 = I oc + I or 2 j .noteq. i h 1 j + w 2 h 2 j 2 , ( 2.
) ##EQU00002##
where I.sub.oc may comprise the power spectral density of a band
limited white noise source, which may simulate outside interference
from neighboring base stations, as measured at the receive antenna
206 of the UE 202a. I.sub.or may comprise the total transmit power
spectral density of a downlink signal received at the UE 202a. The
factor 1/2 may be used to take into account that the total transmit
power may be divided equally among the 2 transmit antennas 238 and
240.
[0051] Consequently, P.sub.s may be represented by the
equation:
P s = E c I or I or SF , ( 3. ) ##EQU00003##
where
E c I or ##EQU00004##
may comprise the power allocation of the signal and SF may comprise
a spreading factor. According to equation (1), the equivalent
channel gain as seen at finger i at the receive antenna 206 of UE
202a may be represented as h.sub.1i+w.sub.2h.sub.2i. The RAKE
receiver of UE 202a may multiply the signal received at each finger
by the conjugate of its corresponding equivalent channel, which may
be represented by the following equation:
y i = ( h 1 i + w 2 h 2 i ) * r i = P s 2 x h 1 i + w 2 h 2 i 2 + (
h 1 i + w 2 h 2 i ) * n i ( 4. ) ##EQU00005##
[0052] Post-multiplication, the RAKE receiver of the UE 202a may
sum, or combine, the signals from all fingers together yielding the
signal at the output of the RAKE receiver. The generated signal at
the output of the RAKE receiver may be represented by the
equation:
y = i y i = P s 2 x i h 1 i + w 2 h 2 i 2 + i n i ( h 1 i + w 2 h 2
i ) * ( 5. ) ##EQU00006##
Therefore, the SINR of the output signal communicated from the
transmit side 200a and received by the UE 202a may be represented
by the equation:
SINR y = P s ( i h 1 i + w 2 h 2 i 2 ) 2 i .sigma. i 2 h 1 i + w 2
h 2 i 2 ( 6. ) ##EQU00007##
[0053] By replacing .sigma..sub.i.sup.2 by its expression in
equation (2), and P.sub.s by its expression in equation (3), SINR
may be expressed by the following resulting equation:
SINR y = E c I or I or SF ( i h 1 i + w 2 h 2 i 2 ) 2 i ( I oc + I
or 2 j .noteq. i h 1 j + w 2 h 2 j 2 ) h 1 i + w 2 h 2 i 2 ( 7. )
##EQU00008##
The numerator and denominator in equation (7) may be normalized by
I.sub.oc, resulting in the following equation for SINR:
[0054] SINR y = E c I or I or I oc SF ( i h 1 i + w 2 h 2 i 2 ) 2 i
( 1 + 1 2 I or I oc j .noteq. i h 1 j + w 2 h 2 j 2 ) h 1 i + w 2 h
2 i 2 , ( 8. ) ##EQU00009##
where I.sub.or/I.sub.oc may be referred to as the geometry of the
system, or system geometry. In instances when the system geometry
and channel impulse responses for the transmit antennas 238 and 240
are known, the value of the weight factor w.sub.2 may be computed
so that the SINR may be maximized.
[0055] In one embodiment of the invention, a search over a
plurality of possible values of w.sub.2 may be utilized, and a
weight value that maximizes the SINR may be selected to be
communicated to the transmit side 200a via the feedback
communication link 201a.
[0056] In instances when the wireless communication system 200
utilizes CLM1, w.sub.2 may comprise a phase shift and may be
represented by the equation w.sub.2=e.sup.j.phi.. In this regard, a
search may be performed by the WVPB 221 for values of .phi. so that
a maximum value of SINR is obtained. In instances when the channel
impulse responses may change from slot to slot, the weight value
w.sub.2 may be re-calculated at each slot. The search for .phi. may
be carried out over the range [0,360].degree., for example, in
quantized steps of X.degree., where X may be equal to, for example,
1, 5, 10, or 45. For example, if X=45, there may be 8 possible
values for .phi.. The SINR may then be computed for each of the 8
values, utilizing equation (8). A value of .phi. that maximizes the
SINR may then be selected.
[0057] In another embodiment of the invention, the wireless
communication system 200 may utilize CLM2. In such instances, SINR
may be represented by the following equation:
SINR y = E c I or I or I oc SF ( i w 1 h 1 i + w 2 h 2 i 2 ) 2 i (
1 + 1 2 I or I oc j .noteq. i w 1 h 1 j + w 2 h 2 j 2 ) w 1 h 1 i +
w 2 h 2 i 2 ( 9. ) ##EQU00010##
[0058] In instances when CLM2 is utilized, the WVPB 221 within the
UE 202a may perform a search over both weight values
w.sub.1=A.sub.1 and
w 2 = A 2 j .phi. . ##EQU00011##
In this regard, the search may be performed over three parameters,
A.sub.1, A.sub.2, .phi.. The search may be quantized to reduce the
number of possible combinations of these three parameters.
[0059] Referring again to FIG. 2, in instances when the wireless
communication system 200 utilizes CLM1 and w.sub.1=1, it may be
assumed that channel impulse responses from both transmit antennas
238 and 240 have the same length. In such instances, each tap, or
channel delay, may be represented by a Rayleigh faded variable.
Taps may have different relative powers and the sum of all taps may
be normalized to unity. Furthermore, for purposes of illustrating
closed loop transmit diversity modes performance, a power
allocation (Ec/Ior) of -16.8 dB and a spreading factor of 128 may
be assumed.
[0060] FIGS. 3A-3D are graphs illustrating closed loop transmit
diversity modes performance via interference suppression in a
wireless system using a RAKE receiver, in accordance with an
embodiment of the invention. Each of FIG. 3x, where x=[a; b; c; d],
illustrate graphs 302x, 304x, and 306x, which represent the mean
SINR at the output of a RAKE receiver, such as a RAKE receiver
within the UE 202a of FIG. 2, as a function of the system geometry
Ior/Ioc. Graph 302x represents the performance of a system with no
diversity where only one transmit antenna is used. Graph 304x
represents the performance of a system with CLM1 diversity where
the weight solution is calculated to maximize the SINR, in
accordance with aspects of the present invention.
[0061] Graph 306x represents the performance of a system with CLM1
diversity where the weight solution is calculated according to a
different criterion, such as to maximize the received power at the
UE 202a. Furthermore, no quantization was applied on the weight
solution generated by the system corresponding to graph 306a, and a
quantization step of X=45 may be applied on the weight solution
generated by the system corresponding to graph 304a. In this
regard, a search over 8 possible values for .phi. may be utilized
to generate the weight solution for the system corresponding to
graph 306a.
[0062] Referring to FIG. 3A, graphs 302a, 304a, and 306a illustrate
closed loop transmit diversity modes performance when the channel
response comprises 2 equal power taps. As illustrated in FIG. 3A,
the gain of CLM1 with prior art technique, graph 306a, over the
1-antenna system, graph 302a, diminishes with increasing system
geometry. However, the gain of CLM1 using the maximized SINR
criterion as illustrated in graph 304a, increases over CLM1 using
the prior art technique of maximizing the receive power, as
illustrated by increasing gaps 310a and 312a. The gain values 310a
and 312a of CLM1 using the maximized SINR criterion over prior art
under these channel conditions may be estimated as 0.65 dB and 1.75
dB, respectively, at system geometry values 5 and 10 dB,
respectively.
[0063] Referring to FIG. 3B, graphs 302a, 304a, and 306a illustrate
closed loop transmit diversity modes performance when the channel
response comprises 2 power taps of relative power [0, -10] dB. As
illustrated in FIG. 3B, the gain of CLM1 using maximizing the SINR
criterion, graph 304b, increases over CLM1 using the prior art
technique of maximizing the receive power, as illustrated by
increasing gaps 310b and 312b.
[0064] Referring to FIG. 3C, graphs 302a, 304a, and 306a illustrate
closed loop transmit diversity modes performance when the channel
response comprises 4 taps of relative power [0, -3, -6, -9] dB. As
illustrated in FIG. 3C, the gain of CLM1 with prior art technique,
graph 306a, over the 1-antenna system, graph 302a, diminishes with
increasing system geometry. However, the gain of CLM1 using the
maximized SINR criterion as illustrated in graph 304c, increases
over CLM1 using the prior art technique of maximizing the receive
power, as illustrated by increasing gaps 310c and 312c. The gain
values 310c and 312c of CLM1 using the maximized SINR criterion
over prior art under these channel conditions may be estimated as
0.33 dB and 0.75 dB, respectively, at system geometry values 5 and
10 dB, respectively.
[0065] Referring to FIG. 3D, graphs 302a, 304a, and 306a illustrate
closed loop transmit diversity modes performance when the channel
response comprises a single tap, in instances of flat fading. As
illustrated in FIG. 3D, both CLM1 performances represented by
graphs 304d and 306d overlap in this case because the criteria of
both methods become equivalent in flat fading. The gain of CLM1
using maximizing the SINR criterion as illustrated in graph 304d,
over the 1-antenna system, graph 302d, is 2.5 dB across the entire
range of system geometry.
[0066] FIG. 4 is a flow diagram illustrating exemplary steps for
processing wireless signals in a WCDMA network equipped with a RAKE
receiver, in accordance with an embodiment of the invention.
Referring to FIGS. 2 and 4, at 402, channel state information and
system geometry information may be acquired by the WVPB 221 for a
wireless signal received via the antenna 206 from the transmit side
200a. At 404, the WVPB 221 may initiate a loop search over a
plurality of weight values. At 406, the WVPB 221 may calculate a
SINR value for a given weight value, based on the channel state
information and/or the system geometry information. At 408, it may
be determined whether all weight values within the loop are
considered. If not all weight values within the loop are
considered, processing may resume at step 406 for a subsequent
weight value. If all weight values within the loop are considered,
at 410, the WVPB 221 may determine a maximum one of the calculated
plurality of SINR values. At 412, the WVPB 221 may feed back to the
transmit side 200a via the link 201a, one or more of the
corresponding plurality of weight values associated with the
determined maximum one of the calculated plurality of SINR
values.
[0067] In an embodiment of the invention, a machine-readable
storage may be provided, having stored thereon, a computer program
having at least one code section executable by a machine, thereby
causing the machine to perform the steps described herein for
processing signals in a wireless communication system so as to
improve CL transmit diversity modes performance via interference
suppression in a WCDMA network equipped with a RAKE receiver.
[0068] Accordingly, the present invention may be realized in
hardware, software, or a combination of hardware and software. The
present invention may be realized in a centralized fashion in at
least one computer system, or in a distributed fashion where
different elements are spread across several interconnected
computer systems. Any kind of computer system or other apparatus
adapted for carrying out the methods described herein is suited. A
typical combination of hardware and software may be a
general-purpose computer system with a computer program that, when
being loaded and executed, controls the computer system such that
it carries out the methods described herein.
[0069] The present invention may also be embedded in a computer
program product, which comprises all the features enabling the
implementation of the methods described herein, and which when
loaded in a computer system is able to carry out these methods.
Computer program in the present context means any expression, in
any language, code or notation, of a set of instructions intended
to cause a system having an information processing capability to
perform a particular function either directly or after either or
both of the following: a) conversion to another language, code or
notation; b) reproduction in a different material form.
[0070] While the present invention has been described with
reference to certain embodiments, it will be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted without departing from the scope of the present
invention. In addition, many modifications may be made to adapt a
particular situation or material to the teachings of the present
invention without departing from its scope. Therefore, it is
intended that the present invention not be limited to the
particular embodiment disclosed, but that the present invention
will include all embodiments falling within the scope of the
appended claims.
* * * * *